10 Weird Things You've Always Wanted to Know About Penises

We admit it, vaginas are tough to figure out, even for those of us who have one. But penises? As straightforward as it may appear, the male member can be pretty damn mysterious. Why is it always hard in the morning? What's with circumcision? What makes it go soft in the middle of sex sometimes? And why is size such a huge issue among otherwise secure guys who should be rocking BDE?

To help you get a handle on all things penis health–related, we consulted doctors who specialize in male sexuality and urology and asked them to shed light on the questions and topics you just don't want to ask about. Behold, 10 fascinating facts about the male member every woman needs to know.

Most erect penises range from 4-6 inches

Guys exaggerate, so science actually looked into this. An analysis of more than 15,000 members from previous penis-size studies found that the average erection length comes in at 5.16 inches, and the average erection girth is 4.59 inches, according to the British Journal of Urology.

When men are smaller or larger than average, it’s not by much. “Almost every man is between 4 and 6 inches, and maybe 15% of men have a penis over 7 inches in length,” Michael Reitano, MD, physician in residence at men’s health company Roman, tells Health.

As for non-erect penises, the same research discovered that the average flaccid length is 3.606 inches and average flaccid girth is 3.665 inches. Dr. Reitano says that there's no correlation between how big a guy is when he's hanging loose and how large he is erect. Some guys are showers...and some are growers.

The male orgasm is a short experience

The typical female orgasm lasts about 20 seconds, according to Dr. Reitano, which makes it three times as long as the average male orgasm—which clocks in at just six seconds, he says. Like the ability to have multiple orgasms and G-spot orgasms, consider this one more orgasmic advantage women have over men.

Sleep hard-ons happen up to 6 times each night

No, it’s not because of sexual dreams. Though the exact reason isn't known, the 4-6 sleep erections a man has each night may be the body's way of keeping things healthy down there, says Natalya Lopushnyan, MD, urologist at Greater Boston Urology. “If men don’t get regular erections, and the penis doesn’t expand regularly, it starts to scar down and actually becomes shorter,” she says. A man with prolonged erectile dysfunction will likely find his penis to be shorter than it used to be, she adds.

Smoking can shave an inch off his penis

As if there aren't enough health risks associated with cigarettes, it's also poison to penises. “Smoking can affect the blood vessels, meaning it can affect [a guy's] ability to have an erection,” says Dr. Reitano. “Even men who have an erection may not be getting as full an erection as they would be if they weren’t smoking.” In fact, a smoker can expect his erect penis to be up to an inch shorter than if he gave up the cigs, he says. Once a guy quits, the true size of his erection will likely return.

The penis is similar to this female organ

In the early stages of embryonic development, the clitoris develops from the same tissue as the penis. “We all have the same parts, it just depends on what hormones we have in our bodies that influence male versus female part development,” says Dr. Lopushnyan. When a destined-to-be-male embryo releases testosterone, that sexual tissue grows and becomes a penis. In the absence of testosterone, the same tissue stays small and becomes the clitoris.

“The tip of the clitoris is also very similar to the head of the penis," says Dr. Lopushnyan. "It’s very sensitive, and honestly if you look at it, it kind of looks the same just smaller.” It also functions in a similar way. “When a woman gets excited, the clitoris becomes larger and gets filled with blood,” she adds.

Circumcised and uncircumcised penises have very few differences

A circumcised penis is one that no longer has a foreskin—a retractable sheath of skin that covers the head of the penis and is surgically removed within days of a boy's birth. Circumcision is common in many cultures around the world, though rates are on the decline in the U.S. The American Academy of Pediatrics recommends that newborn boys be circumcised because circumcision has been linked to lower rates of STIs and other infections. But ultimately it comes down to parental choice.

Other than appearance, Dr. Lopushnyan says there’s not much difference between circumcised and uncircumcised penises. When an uncircumcised man gets an erection, the foreskin folds back and the head is exposed, so you won’t notice a difference during sex.

A broken penis is hella serious

A boner doesn't actually contain a bone, of course. But penile fracture is a real (and very, very painful) thing. The fibrous, blood-filled tissue inside an erect penis can tear if a guy thrusts against something too forcefully, says Dr. Lopushnyan. When it tears, “all of that blood comes out and stays under the skin, so you very quickly get this huge bruise and a lot of swelling,” she explains. Dr. Lopushnyan says a fractured penis turns purple, swells, and resembles an eggplant. (We're never using that eggplant emoji again.)

Positions that have his female partner coming straight down on his penis, like woman on top, put a guy at the greatest risk for fracture. Take it slow, cowgirl, and spare him the agony and emergency trip to the ER. If a broken penis isn't addressed immediately, it can result in permanent damage.

An erection offers clues to a guy's health

Dr. Lopushnyan says men need two key things to have an erection (other than a penis, obviously): healthy blood vessels to carry blood to the penis, and healthy nerves to signal those blood vessels to start pumping. Without these, a guy will have erectile dysfunction (ED)—which typically means he has trouble maintaining an erection or can't get it up at all.

Heart disease, diabetes, high blood pressure, and other potentially life-threatening issues can cause ED because they affect blood vessels, so any man who finds himself suffering from ED should see a doctor, stat. ED can also be the result of stress, depression, and anxiety. If a physical workup comes out normal, a mental health evaluation might be in order.

Morning wood is a good sign

Waking up with a hard-on is a normal thing for guys; it has nothing to do with how horny he is but the biological fact that testosterone levels are highest in the a.m. If a man stops having morning erections, however, it could mean that something's up with his health. Two weeks without one necessitates a trip to a doctor, suggests Dr. Reitano.

The lack of morning wood could have to do with hormone levels, blood vessels, or his mental health, among other possibilities. “It’s so important that men realize an erection is more than just something that happens based on their being able to be sexually active, but it’s based on being healthy individuals who are taking care of every organ system,” says Dr. Reitano.

A semen allergy is rare—but real

It's very uncommon, but an allergy to semen (or more precisely, an allergy to the proteins in semen) is a real medical condition. Signs his female partner should look for include burning, itching, redness and vaginal discomfort 10 to 30 minutes following unprotected sex, says Dr. Lopushnyan. It might happen the first time you have sex, or it could develop years later.

A semen allergy is often misdiagnosed as a yeast infection or an STI, according to the International Society for Sexual Medicine. If you're noticing these signs, try having sex with a condom. If the symptoms don't appear, his semen might be the culprit. While it can a major relationship buzzkill, it is possible to have kids with a guy whose semen you're allergic to with the help of in vitro fertilization, says Dr. Lopushnyan.